9 Doping in CVD for EPITAXY Intentional and UnintentionalThe dopant sources at the surface go through:dissociation of hydride gaslattice site incorporationburying of dopants by other atoms in the filmAutodoping: 1 - 4Si source + Dopant (AsH3, PH3, or B2H6)Simulation very inaccurate : chamber design etc.In deposition , the doping,°CoutdiffusionautodopingoutdiffusionT&time of CVDautodopingThe growth is faster than the diffusionCalculate all distributions (=contributions) to get C(x,t)

17 DC SputteringLow concentrations of electrons -> few collisions -> large voltage here0.1 –10 mme-The source of material to be depositedI+low e--conc.e- collide with Ar atomsexcitation=glowConductive !Ar ions (+) strike the target and sputter ions  electrons do not have high energy yet dark glow anode sheath.(Crookes dark space)ions+ potentialpositive potential (form next to each surface = anode)I+ and e- strike the surface:µe larger (smaller mass than for ions)more electrons than ionsE field due to charge imbalance Vp (10 V develops) to decrease e- accumulationIons get neutralized by e- and diffuse to the wafer surfacesecondary electrons!They sustain the plasmaVery small sputtering at the anode  can be used for bias sputtering and ionized sputtering